A continuously variable transmission having driving and driven pulley assemblies with a belt entrained thereabout to interconnect the pulley assemblies is known in the art. In such an arrangement, each pulley assembly comprises an axially fixed sheave or pulley member fixed on its associated shaft and a complimentary axially movable sheave or pulley member slidably arranged on its associated shaft. The axially movable sheave or pulley member is controllably moved toward and away from the other sheave to change the drive ratio between the driving shaft and the driven shaft. The driven shaft may be interconnected to a differential by a gear mechanism. Two output shafts usually extend from the differential to the drive wheels of the vehicle.
S. Yamamuro et al U.S. Pat. No. 4,484,493 discloses one example of a continuously variable transmission. The Yamamuro device includes a torque converter disposed between an engine and a pair of pulley assemblies. As such, the driven pulley in the pair of pulley assemblies has applied thereto a multiple of the engine torque as controlled by the torque converter. The driving and driven pulley assemblies are drivingly connected to a differential through a gear mechanism. The gear mechanism of the Yamamuro et al device includes a one gear forward drive path controlled by a clutch mechanism and a three gear reverse drive path also controlled by a clutch mechanism. Both of the gear paths mesh with a ring gear of a differential mechanism. The vehicle's direction is controlled through selective operation of one or the other of the two clutch assemblies.
The Yamamuro et al disclosure suggests that such an arrangement provides design advantages regarding the overall size of the transmission. Although this may be true, the disclosed transmission is not without its drawbacks. More specifically, the disclosed gear drive mechanism for connecting the driven shaft to the differential severely restricts or limits this device. That is, the one gear forward drive path of the drive mechanism inherently causes the engine output drive member to rotate in a direction opposite to that of the output shafts of the differential. With a transmission constructed in accordance with the Yamamuro et al teachings, the output shafts extending from the differential for driving the wheels are rotatably driven in a direction opposite to the rotary direction of the engine in a forward mode of operation. In practice, the vast majority of today's cars are designed to have the engine and its drive wheels turn in the same direction in the forward operative mode. Accordingly, and without some major redesign efforts, the Yamamuro et al device does not lend itself to the vast majority of today's vehicles. As is apparent from further analysis, the drive mechanism of the Yamamuro et al device lacks any possibility for change. That is, because the one gear forward path and the three gear reverse path both engage the ring gear of the differential, neither the gears comprising the drive mechanism nor the ring gear can be interchanged to improve the effective drive ratios of either the drive mechanism or the differential. From a design standpoint, it would be beneficial to have the capability of modulating drive ratios through the driven and drive pulley assemblies as well as through the gear mechanism and the differential. The Yamamuro et al device lacks this capability.